Semiconductor device models including re-usable sub-structures

ABSTRACT

Methods and tools for generating measurement models of complex device structures based on re-useable, parametric models are presented. Metrology systems employing these models are configured to measure structural and material characteristics associated with different semiconductor fabrication processes. The re-useable, parametric sub-structure model is fully defined by a set of independent parameters entered by a user of the model building tool. All other variables associated with the model shape and internal constraints among constituent geometric elements are pre-defined within the model. In some embodiments, one or more re-useable, parametric models are integrated into a measurement model of a complex semiconductor device. In another aspect, a model building tool generates a re-useable, parametric sub-structure model based on input from a user. The resulting models can be exported to a file that can be used by others and may include security features to control the sharing of sensitive intellectual property with particular users.

CROSS REFERENCE TO RELATED APPLICATION

The present application for patent claims priority under 35 U.S.C. §119from U.S. provisional patent application Ser. No. 61/927,832, entitled“Building Optical Metrology Models Based on Structure and ApplicationDelineated Characteristics,” filed Jan. 15, 2014, the subject matter ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The described embodiments relate to metrology systems and methods, andmore particularly to methods and systems for improved measurementaccuracy.

BACKGROUND INFORMATION

Semiconductor devices such as logic and memory devices are typicallyfabricated by a sequence of processing steps applied to a specimen. Thevarious features and multiple structural levels of the semiconductordevices are formed by these processing steps. For example, lithographyamong others is one semiconductor fabrication process that involvesgenerating a pattern on a semiconductor wafer. Additional examples ofsemiconductor fabrication processes include, but are not limited to,chemical-mechanical polishing, etch, deposition, and ion implantation.Multiple semiconductor devices may be fabricated on a singlesemiconductor wafer and then separated into individual semiconductordevices.

Optical metrology processes are used at various steps during asemiconductor manufacturing process to detect defects on wafers topromote higher yield. Optical metrology techniques offer the potentialfor high throughput without the risk of sample destruction. A number ofoptical metrology based techniques including scatterometry andreflectometry implementations and associated analysis algorithms arecommonly used to characterize critical dimensions, film thicknesses,composition and other parameters of nanoscale structures.

As devices (e.g., logic and memory devices) move toward smallernanometer-scale dimensions, characterization becomes more difficult.Devices incorporating complex three-dimensional geometry and materialswith diverse physical properties contribute to characterizationdifficulty.

In response to these challenges, more complex optical tools have beendeveloped. Measurements are performed over a large ranges of severalmachine parameters (e.g., wavelength, azimuth and angle of incidence,etc.), and often simultaneously. As a result, the measurement time,computation time, and the overall time to generate reliable results,including measurement recipes, increases significantly.

In addition, existing model based metrology methods typically include aseries of steps to model and then measure structure parameters.Typically, measurement data (e.g., DOE spectra) is collected from aparticular metrology target. An accurate model of the optical system,dispersion parameters, and geometric features is formulated. Inaddition, simulation approximations (e.g., slabbing, Rigorous CoupledWave Analysis (RCWA), etc.) are performed to avoid introducingexcessively large errors. Discretization and RCWA parameters aredefined. A series of simulations, analysis, and regressions areperformed to refine the geometric model and determine which modelparameters to float. A library of synthetic spectra is generated.Finally, measurements are performed using the library or regression inreal time with the geometric model.

Currently, models of device structures being measured are assembled by auser of a measurement modeling tool from primitive structural buildingblocks. These primitive structural building blocks are simple geometricshapes (e.g., square frusta) that are assembled together to approximatemore complex structures. The primitive structural building blocks aresized by the user based on user input that specifies the shape detailsof each primitive structural building block. In one example, eachprimitive structural building block includes an integrated customizationcontrol panel where a user inputs specific parameters that determine theshape details. Similarly, primitive structural building blocks arejoined together by constraints that are also manually entered by theuser. For example, the user enters a constraint that ties a vertex ofone primitive building block to a vertex of another building block. Thisallows the user to build models that represent a series of the actualdevice geometries when the size of one building block changes.User-defined constraints between primitive structural building blocksenable broad modeling flexibility. For example, the thicknesses orheights of different primitive structural building blocks can beconstrained to a single parameter in multi-target measurementapplications. Furthermore, primitive structural building blocks havesimple geometric parameterizations which the user can constrain toapplication-specific parameters. For example, the sidewall angle of aresist line can be manually constrained to parameters representing thefocus and dose of a lithography process.

Although models constructed from primitive structural building blocksoffer a wide range of modeling flexibility and user control, the modelbuilding process becomes very complex and error prone when modelingcomplex device structures. A user needs to assemble primitive structuralbuilding blocks together accurately, ensure they are correctlyconstrained, and parameterize the model in a geometrically consistentmanner. Accomplishing this is not an easy task, and users spendsignificant amounts of time ensuring that their models are correct. Inmany cases, users do not realize their models are inconsistent andincorrect because it is difficult to comprehend how all of the primitivestructural building blocks change shape and location in parameter space.Specifically, it is very difficult to determine if models that arestructurally consistent for a given set of parameter values remainstructurally consistent for another set of parameter values.

FIG. 1A depicts twelve different primitive structural building blocks11-22 assembled together to form an optical critical dimension (OCD)model 10 depicted in FIG. 1B. Each primitive structural building blockis rectangular in shape. To construct OCD model 10 a user must manuallydefine the desired dimensions, constraints, and independent parameters(e.g., parameters subject to variation) of the model. Models constructedbased on primitive structural building blocks (i.e., basic shapes suchas rectangles) typically require a large number of primitives,constraints, and independent parameters for which the user must defineranges of variation. This makes model-building very complex and prone touser errors.

Furthermore, model complexity makes it difficult for one user tounderstand models built by another. The user needs to be able tounderstand the intent of the original model owner and this becomesincreasingly challenging as the number of primitive structural buildingblocks, constraints, and independent parameters increases. Consequently,transferring ownership of models (e.g., from applications engineers toprocess engineers) is a time consuming, difficult process. In manycases, the complexity of the models leads to frustration amongstcolleagues, and in some cases, prevents the transfer process from everbeing fully completed. In some examples, a user generates a new modelfrom primitive structural building blocks to mimic a model generated bya colleague. In many cases the resulting model is slightly different,and therefore delivers slightly different results due to thenon-commutative property of floating point operations on computers. Insome other examples, a user surrenders or risks intellectual property byhaving another firm develop the model.

Optical metrology structures have in the past remained simple enoughthat new models are commonly designed for each project. However, withincreasingly complicated models and less time per project, improvedmodeling methods and tools are desired.

SUMMARY

Methods and tools for generating measurement models of complex devicestructures based on re-useable, parametric models are presented.Metrology systems employing these models are configured to measurestructural and material characteristics (e.g., material composition,dimensional characteristics of structures and films, etc.) associatedwith different semiconductor fabrication processes.

In one aspect, a model building tool includes re-useable, parametricmodels of complex device sub-structures that are useable as buildingblocks in a model of a complex semiconductor device. This makes themodel building process more intuitive and less error-prone. Furthermore,because the re-useable, parametric sub-structure models are optimizedfor specific structures and measurement applications, the resultingdiscretized measurement model is computationally more efficient thantraditional models. In addition, the parametric sub-structure models canbe saved and shared among different projects and different users.

In a further aspect, the re-useable, parametric sub-structure model isfully defined by the values of the independent parameters entered by theuser of the model building tool. All other variables associated with themodel shape and internal constraints among constituent geometricelements are pre-defined within the model. Thus, beyond the values ofthe independent parameters, no other user input is required to fullydefine the re-useable, parametric sub-structure model. This greatlysimplifies the model building process.

In another further aspect, a model building tool integrates one or morere-useable, parametric models into a measurement model of a complexsemiconductor device. In some embodiments, a measurement model of asemiconductor device is fully described by one re-useable, parametricmodel. In some other embodiments, a measurement model of a semiconductordevice is fully described by a combination of two or more re-useable,parametric models.

In another aspect, a model building tool generates a re-useable,parametric sub-structure model based on input from a user. In someembodiments, a model building tool generates a re-useable, parametricsub-structure model based on a composition of a number of simplergeometric primitives, or simpler re-useable, parametric sub-structuremodels indicated by a user. The composition changes the collection ofindividual models into a single re-useable, parametric sub-structuremodel that can be used as an element of a measurement model as if it isa primitive building block.

Re-useable, parametric sub-structure models can be generated indifferent ways. In one example, a user directs the model building toolto combine and constrain one or more geometric primitives, one or moreexisting sub-structure models, or any combination by user-generatedcomputer code. In another example, a re-useable, parametricsub-structure model is based on more complex geometric structures, andthus is an amalgamation of fewer, more complex geometric primitives. Inyet another example, a user may interact with a graphical user interface(GUI) that allows a user to select one or more geometric primitives, oneor more existing sub-structure models, or any combination, and thenindicate the users desire to group these elements together and selectthe desired independent parameters. In response the model building toolautomatically generates the appropriate constraints to realize a fullyintegrated parametric sub-structure model.

In another further aspect, the user can export a newly createdparametric sub-structure model into a file that can be used by others.In another example, a newly created parametric sub-structure model canbe listed in the model building tool as an available building block thatcan be selected by a user to construct a measurement model, or yetanother, more complex parametric sub-structure model.

In another further aspect, the model building tool generates and makesavailable for use, re-useable, parametric models of complex devicesub-structures that include key characteristics of specificsemiconductor processes embedded into their design. More specifically, are-usable, parametric sub-structure model includes controls that allowthe user to specify wafer artifacts created by one or more processsteps.

In another further aspect, the model building tool generates and makesavailable for use, re-useable, parametric models of complex devicesub-structures that include measurement application specific details(e.g., constraints, dimensions, etc. that derive from particularapplications).

In yet another aspect, the model building tool includes securityfeatures to control the sharing of sensitive intellectual property withparticular users.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrative of twelve different primitivestructural building blocks 11-22 assembled together to form an opticalcritical dimension (OCD) model 10 depicted in FIG. 1B.

FIG. 1B is a diagram illustrative of an optical critical dimension (OCD)model 10.

FIG. 2 is a diagram illustrative of a system 100 for measuringcharacteristics of a semiconductor wafer.

FIG. 3 is a diagram illustrative of a re-usable, parametricsub-structure model 200 representing three conformal layers of a trenchstructure.

FIG. 4 is a diagram illustrative of a combination of geometricprimitives with a re-useable, parametric sub-structure model to form themeasurement model depicted in FIG. 5.

FIG. 5 is a diagram illustrative of a measurement model formed from thecombination of geometric primitives and a re-useable, parametricsub-structure model depicted in FIG. 4.

FIG. 6 is a diagram illustrative of a re-usable, parametricsub-structure model 210 representing three conformal layers of a trenchstructure in another embodiment.

FIGS. 7A-7D depict four basic manufacturing process steps employed togenerate a semiconductor device structure.

FIG. 8 depicts a re-usable, parametric sub-structure model 230 of astacked device structure.

FIG. 9 depicts two different re-useable, parametric sub-structure models231 and 232 combined into a fully integrated parametric sub-structuremodel 233 by a model building tool as described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

Methods and tools for generating measurement models of complex devicestructures based on re-useable, parametric models are presented.Metrology systems employing these models are configured to measurestructural and material characteristics (e.g., material composition,dimensional characteristics of structures and films, etc.) associatedwith different semiconductor fabrication processes.

FIG. 2 illustrates a system 100 for measuring characteristics of asemiconductor wafer. As shown in FIG. 2, the system 100 may be used toperform spectroscopic ellipsometry measurements of one or morestructures 114 of a semiconductor wafer 112 disposed on a waferpositioning system 110. In this aspect, the system 100 may include aspectroscopic ellipsometer equipped with an illuminator 102 and aspectrometer 104. The illuminator 102 of the system 100 is configured togenerate and direct illumination of a selected wavelength range (e.g.,150-1700 nm) to the structure 114 disposed on the surface of thesemiconductor wafer 112. In turn, the spectrometer 104 is configured toreceive light from the surface of the semiconductor wafer 112. It isfurther noted that the light emerging from the illuminator 102 ispolarized using a polarization state generator 107 to produce apolarized illumination beam 106. The radiation reflected by thestructure 114 disposed on the wafer 112 is passed through a polarizationstate analyzer 109 and to the spectrometer 104. The radiation receivedby the spectrometer 104 in the collection beam 108 is analyzed withregard to polarization state, allowing for spectral analysis ofradiation passed by the analyzer. These spectra 111 are passed to thecomputing system 116 for analysis of the structure 114.

In a further embodiment, the metrology system 100 is a measurementsystem 100 that includes one or more computing systems 116 configured toexecute model building tool 130 in accordance with the descriptionprovided herein. In the preferred embodiment, model building tool 130 isa set of program instructions 120 stored on a carrier medium 118. Theprogram instructions 120 stored on the carrier medium 118 are read andexecuted by computing system 116 to realize model building functionalityas described herein. The one or more computing systems 116 may becommunicatively coupled to the spectrometer 104. In one aspect, the oneor more computing systems 116 are configured to receive measurement data111 associated with a measurement (e.g., critical dimension, filmthickness, composition, process, etc.) of the structure 114 of specimen112. In one example, the measurement data 111 includes an indication ofthe measured spectral response of the specimen by measurement system 100based on the one or more sampling processes from the spectrometer 104.In some embodiments, the one or more computing systems 116 are furtherconfigured to determine specimen parameter values of structure 114 frommeasurement data 111. In one example, the one or more computing systems116 are configured to access model parameters in real-time, employingReal Time Critical Dimensioning (RTCD), or it may access libraries ofpre-computed models for determining a value of at least one specimenparameter value associated with the target structure 114.

In addition, in some embodiments, the one or more computing systems 116are further configured to receive user input 113 from a user inputsource 103 such as a graphical user interface, keyboard, etc. The one ormore computer systems are further configured to configure re-useable,parametric sub-structure models as described herein.

In some embodiments, measurement system 100 is further configured tostore one or more re-useable, parametric sub-structure models 115 in amemory (e.g., carrier medium 118).

It should be recognized that the various steps described throughout thepresent disclosure may be carried out by a single computer system 116or, alternatively, a multiple computer system 116. Moreover, differentsubsystems of the system 100, such as the spectroscopic ellipsometer101, may include a computer system suitable for carrying out at least aportion of the steps described herein. Therefore, the aforementioneddescription should not be interpreted as a limitation on the presentinvention but merely an illustration. Further, the one or more computingsystems 116 may be configured to perform any other step(s) of any of themethod embodiments described herein.

The computing system 116 may include, but is not limited to, a personalcomputer system, mainframe computer system, workstation, image computer,parallel processor, or any other device known in the art. In general,the term “computing system” may be broadly defined to encompass anydevice having one or more processors, which execute instructions from amemory medium. In general, computing system 116 may be integrated with ameasurement system such as measurement system 100, or alternatively, maybe separate from any measurement system. In this sense, computing system116 may be remotely located and receive measurement data and user input113 from any measurement source and user input source, respectively.

Program instructions 120 implementing methods such as those describedherein may be transmitted over or stored on carrier medium 118. Thecarrier medium may be a transmission medium such as a wire, cable, orwireless transmission link. The carrier medium may also include acomputer-readable medium such as a read-only memory, a random accessmemory, a magnetic or optical disk, or a magnetic tape.

In addition, the computer system 116 may be communicatively coupled tothe spectrometer 104 or the illuminator subsystem 102 of theellipsometer 101, or the user input source 103 in any manner known inthe art.

The computing system 116 may be configured to receive and/or acquiredata or information from the user input source 103 and subsystems of thesystem (e.g., spectrometer 104, illuminator 102, and the like) by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe computer system 116, user input source 103, and other subsystems ofthe system 100. Further, the computing system 116 may be configured toreceive measurement data via a storage medium (i.e., memory). Forinstance, the spectral results obtained using a spectrometer ofellipsometer 101 may be stored in a permanent or semi-permanent memorydevice (not shown). In this regard, the spectral results may be importedfrom an external system. Moreover, the computer system 116 may send datato external systems via a transmission medium.

The embodiments of the system 100 illustrated in FIG. 2 may be furtherconfigured as described herein. In addition, the system 100 may beconfigured to perform any other block(s) of any of the methodembodiment(s) described herein.

Optical metrology for critical dimensions (CDs), thin film thicknesses,optical properties and compositions, overlay, lithography focus/dose,etc. typically requires a geometric model of the underlying structure tobe measured. This measurement model includes the physical dimensions,material properties, and parameterization of the structure.

In one aspect, a model building tool includes re-useable, parametricmodels of complex device sub-structures that are useable as buildingblocks in a model of a complex semiconductor device. This makes themodel building process more intuitive and less error-prone. Furthermore,because the re-useable, parametric sub-structure models are optimizedfor specific structures and measurement applications, the resultingdiscretized measurement model is computationally more efficient thantraditional models. In addition, the parametric sub-structure models canbe saved and shared among different projects and different users.

In a further aspect, the re-useable, parametric sub-structure model isfully defined by the values of the independent parameters entered by theuser of the model building tool. All other variables associated with themodel shape and internal constraints among constituent geometricelements are pre-defined within the model. Thus, beyond the values ofthe independent parameters, no other user input is required to fullydefine the re-useable, parametric sub-structure model. This greatlysimplifies the model building process.

In some embodiments, the re-useable, parametric sub-structure models arestructure-specific. FIG. 3 depicts a re-usable, parametric sub-structuremodel 200 representing three conformal layers of a trench structure. Asdepicted in FIG. 3, the independent parameters that define the shape ofthe model are the thicknesses of each layer, T₁, T₂, and T₃, the widthof the trench, W, and the depth of the trench, H. Optionally, materialparameters associated each of the layers may be defined as independentvariables that can be defined by a user.

A user of the model building tool only needs to enter the values ofthese five parameters to fully define the geometry of this re-useable,parametric sub-structure model 200. All of the other variablesassociated with the model shape and internal constraints are pre-definedwithin the model, and no further input is required to fully define theshape of model 210.

In contrast, the structural model depicted in FIG. 1A requires thedefinition of nine different primitive elements (elements 12-20) andtheir interrelationships (e.g., constraints among each of the elements)to model a similar trench structure having three conformal layers. Theuser needs to define, combine, constrain, and parameterize these nineelements manually. For example, the user would have to constrain theright side of each of elements 12, 13, and 14 to align with the leftside of elements 20, 19, and 18, respectively. Similarly, the user wouldhave to constrain the left side of each of elements 15, 16, and 17 withthe right side of elements 18, 19, and 20, respectively. In addition,the user would have to constrain the height of each of elements 18, 19,and 20 to be equal to the width of the side pieces 14 and 15, 13 and 16,and 12 and 17, respectively. These constraint examples are just a subsetof an even larger set of constraints that must be established by theuser to fully define a simple trench structure having three conformallayers. Thus, it is not difficult to imagine the difficulty associatedwith defining a model of a complex device structure using only simplegeometric primitives. As depicted in FIG. 3, a single re-useable,parametric sub-structure model 200 that is fully defined by only fiveindependent parameters replaces a model that includes nine geometricprimitives and dozens of constraints and shape parameter values.

In another further aspect, a model building tool integrates one or morere-useable, parametric models into a measurement model of a complexsemiconductor device. As depicted in FIG. 4, a model building toolreceives input from a user to combine geometric primitives 11, 21, and22 with re-useable, parametric sub-structure model 200 to form ameasurement model 205 depicted in FIG. 5. In some other embodiments, ameasurement model of a semiconductor device is fully described by onere-useable, parametric model. In some other embodiments, a measurementmodel of a semiconductor device is fully described by a combination oftwo or more re-useable, parametric models.

In another aspect, a model building tool generates a re-useable,parametric sub-structure model based on input from a user.

In some embodiments, a model building tool generates a re-useable,parametric sub-structure model based on a composition of a number ofsimpler geometric primitives, or simpler re-useable, parametricsub-structure models indicated by a user. The composition changes thecollection of individual models into a single re-useable, parametricsub-structure model that can be used as an element of a measurementmodel as if it is a primitive building block.

As depicted in FIG. 3, nine geometric primitives (e.g., rectangularshapes) are fully integrated into a sub-structure model that is fullydefined by five independent parameters. The model building tool savesthe sub-structure model for later use. Internally, the sub-structuremodel includes the constraints necessary to fully integrate the ninegeometric primitives. These constraints are saved as part of thesub-structure model and are enforced at every instance of thesub-structure model. In this manner, users can create a collection ofcommonly used complex shapes with pre-defined constraints. Thesub-structure model can be unloaded and saved into files, reloaded intoa project and used, and shared among users.

The re-useable, parametric sub-structure models generated by the modelbuilding tool enable a user or group of users to generate a library ofsub-structures that can be reused. Different users who use differentinstances of the same sub-structure model can expect to achieve the samenumerical results.

Re-useable, parametric sub-structure models can be generated indifferent ways. In one example, a user directs the model building toolto combine and constrain one or more geometric primitives, one or moreexisting sub-structure models, or any combination by user-generatedcomputer code. FIG. 6 depicts a re-useable, parametric sub-structuremodel 210 assembled based on user-generated computer code that isdefined by its independent parameters, T₁, T₂, T₃, W, and H, in a mannersimilar to model 200 depicted in FIG. 3. However, re-useable, parametricsub-structure model 210 is based on more complex geometric structures(U-shapes), and thus is an amalgamation of fewer, more complex geometricprimitives. As a result, model 210 includes fewer vertices than model200. This results in a smoother model discretization that yields a morecomputationally efficient measurement model due to a reduced number ofdiscretization points. In general, models that contain fewer geometricbuilding blocks and fewer constraints results in a faster discretizationas the discretization engine no longer needs to parse through so manygeometric building blocks and constraints. In some embodiments, thediscretization points of a first re-useable, parametric model arealigned with the discretization points of a second re-useable,parametric model within a floating point precision of the underlyingcomputing system to ensure repeatable computational results from thecombined model.

In some other examples, a user may interact with a graphical userinterface (GUI) that allows a user to select one or more geometricprimitives, one or more existing sub-structure models, or anycombination, and then indicate the users desire to group these elementstogether and select the desired independent parameters. In response themodel building tool automatically generates the appropriate constraintsto realize a fully integrated parametric sub-structure model. The usercan then export the newly created parametric sub-structure model into afile that can be used by others. In another example, the newly createdparametric sub-structure model can be listed in the model building toolas an available building block that can be selected by a user toconstruct a measurement model, or yet another, more complex parametricsub-structure model. The re-usable parametric sub-structure models allowmultiple users to collaboratively work on different parts of a complexmodel and assembly them together at the final stage.

FIG. 9 depicts two different re-useable, parametric sub-structure models231 and 232. In one example, a user may interact with a graphical userinterface (GUI) that allows the user to select models 231 and 232 andspecify the desire to group these elements together with model 231located on top of model 232. In response the model building toolautomatically generates the appropriate constraints to realize fullyintegrated parametric sub-structure model 233. The user can then exportthe newly created parametric sub-structure model into a file that can beused by others.

The number of components required to assemble a complex device model issignificantly reduced by combining two or more re-useable, parametricsub-structure models, rather than geometric primitives. Moreover, thenumbers of relationships among the components that must be specified bythe user are also significantly reduced. This simplifies the initialmodel building process, makes it less error-prone, and makes it easierto transfer models between different users.

In another further aspect, the model building tool generates and makesavailable for use, re-useable, parametric models of complex devicesub-structures that include key characteristics of specificsemiconductor processes embedded into their design. More specifically, are-usable, parametric sub-structure model includes controls that allowthe user to specify wafer artifacts created by one or more processsteps.

FIGS. 7A-7D depict four basic manufacturing process steps to generatethe structure depicted in FIG. 7D. First, a film 22 of thickness, T, isdeposited on a substrate 221 as depicted in FIG. 7A. Next, a trench ofwidth, W, is etched into the film layer 222 as depicted in FIG. 7B.Next, materials 223, 224, and 225, are conformally deposited over thefilm and trench as depicted in FIG. 7C. Finally, the structure isplanarized to a height, T_(p), as depicted in FIG. 7D.

In one embodiment, a re-useable, parametric model represents all four ofthese steps. Furthermore, the user is able to select which process stepto model. For example, if a user wants to first model the trench etchprocess step, the user controls the re-useable, parametric model toinclude the processes needed to create the trench etch (i.e., the filmdeposition and trench etch steps). The user would define the materialused in the film deposition step, define the thickness of the depositedfilm, and define the dimensions of the trench. If the user wants tomodel the planarization step, the user starts with the previouslydefined trench etch model and then controls the re-useable, parametricmodel to include the processes needed to create the planarized structure(i.e., the conformal deposition and planarization steps). The user woulddefine the number of conformal depositions and the materials/thicknessesfor each deposition define the depth of the planarization. In thismanner, the user is able to individually control each of the processsteps represented by the re-useable, parametric model. Thus, a singlemodel can be utilized to measure multiple process steps.

In some lithography focus/dose applications, resist lines of stackeddevice structures are modeled as stacked trapezoids that are constrainedin the following manner: 1) the top critical dimension (TCD) and bottomcritical dimension (BCD) of adjacent trapezoids are constrained to beequal, 2) the heights of the individual trapezoids are constrained to beequal, 3) the individual critical dimensions are constrained to befunctions of user-defined focus and dose parameters, and 4) the heightof the individual trapezoids is constrained to be a function of theaforementioned focus and dose parameters. Traditionally, all of theseconstraints need to be set by the user.

In another further aspect, the model building tool generates and makesavailable for use, re-useable, parametric models of complex devicesub-structures that include measurement application specific details(e.g., constraints, dimensions, etc. that derive from particularapplications).

FIG. 8 depicts a re-usable, parametric sub-structure model 230 of astacked device structure. In this example, the model building tool readsa file that contains the equations of the individual CDs and heights.This file is typically generated by a lithography simulator such asPROLITH software available from KLA-Tencor Corporation, Milpitas, Calif.(USA). Based on this application information the model building toolautomatically sets the parameterization and constraints of there-usable, parametric sub-structure model 230.

In another example, the model building tool can also be employed togenerate re-usable, parametric sub-structure models that describe fieldenhancement elements used in some optical metrology applications. Fieldenhancement elements are described in further detail in U.S. Pat. No.8,879,073 assigned to KLA-Tencor Corporation, the subject matter ofwhich is incorporated herein by reference its entirety. The modelbuilding tool can be employed to generated re-usable, parametricsub-structure models for each type of field enhancement element anddifferent applications.

In yet another example, the model building tool can also be employed togenerate re-usable, parametric sub-structure models that describemetrology targets generated by metrology target design or overlay designsoftware. In one example, the model building tool receives graphicaldatabase system (GDS) data generated by a software simulator andautomatically generates re-usable, parametric sub-structure models thatpredicts the morphology of spacer pitch splitting.

In yet another aspect, the model building tool includes securityfeatures to control the sharing of sensitive intellectual property withparticular users. For example, it may be desireable an entity to share ameasurement model with another entity, but without sharing particularaspects of the measurement model that include sensitive intellectualproperty. In some examples, the model building tool allows a user tohide all or part of one or more re-useable, parametric sub-structuremodels from display to allow the models to be shared with otherentities. In some examples, the model building tool allows a user toomit all or part of one or more re-useable, parametric sub-structuremodels to prevent sharing of these sensitive elements with anotherentity. In some other examples, the model building tool allows a user toinclude password protection to control access to all or part of one ormore re-useable, parametric sub-structure models to limit the sharing ofsensitive elements to authorized entities. In this manner, sensitiveintellectual property embodied in certain features of the re-useable,parametric sub-structure models can be kept private by the user.

Although the methods discussed herein are explained with reference tosystem 100, any optical metrology system configured to illuminate anddetect light reflected, transmitted, or diffracted from a specimen maybe employed to implement the exemplary methods described herein.Exemplary systems include an angle-resolved reflectometer, ascatterometer, a reflectometer, an ellipsometer, a spectroscopicreflectometer or ellipsometer, a beam profile reflectometer, amulti-wavelength, two-dimensional beam profile reflectometer, amulti-wavelength, two-dimensional beam profile ellipsometer, a rotatingcompensator spectroscopic ellipsometer, etc. By way of non-limitingexample, an ellipsometer may include a single rotating compensator,multiple rotating compensators, a rotating polarizer, a rotatinganalyzer, a modulating element, multiple modulating elements, or nomodulating element.

It is noted that the output from a source and/or target measurementsystem may be configured in such a way that the measurement system usesmore than one technology. In fact, an application may be configured toemploy any combination of available metrology sub-systems within asingle tool, or across a number of different tools.

A system implementing the methods described herein may also beconfigured in a number of different ways. For example, a wide range ofwavelengths (including visible, ultraviolet, infrared, and X-ray),angles of incidence, states of polarization, and states of coherence maybe contemplated. In another example, the system may include any of anumber of different light sources (e.g., a directly coupled lightsource, a laser-sustained plasma light source, etc.). In anotherexample, the system may include elements to condition light directed toor collected from the specimen (e.g., apodizers, filters, etc.).

As described herein, the term “critical dimension” includes any criticaldimension of a structure (e.g., bottom critical dimension, middlecritical dimension, top critical dimension, sidewall angle, gratingheight, etc.), a critical dimension between any two or more structures(e.g., distance between two structures), a displacement between two ormore structures (e.g., overlay displacement between overlaying gratingstructures, etc.), and a dispersion property value of a material used inthe structure or part of the structure. Structures may include threedimensional structures, patterned structures, overlay structures, etc.

As described herein, the term “critical dimension application” or“critical dimension measurement application” includes any criticaldimension measurement.

As described herein, the term “metrology system” includes any systememployed at least in part to characterize a specimen in any aspect.However, such terms of art do not limit the scope of the term “metrologysystem” as described herein. In addition, the metrology system 100 maybe configured for measurement of patterned wafers and/or unpatternedwafers. The metrology system may be configured as a LED inspection tool,edge inspection tool, backside inspection tool, macro-inspection tool,or multi-mode inspection tool (involving data from one or more platformssimultaneously), and any other metrology or inspection tool thatbenefits from the calibration of system parameters based on criticaldimension data.

Various embodiments are described herein for a semiconductor processingsystem (e.g., an inspection system or a lithography system) that may beused for processing a specimen. The term “specimen” is used herein torefer to a site, or sites, on a wafer, a reticle, or any other samplethat may be processed (e.g., printed or inspected for defects) by meansknown in the art. In some examples, the specimen includes a single sitehaving one or more measurement targets whose simultaneous, combinedmeasurement is treated as a single specimen measurement or referencemeasurement. In some other examples, the specimen is an aggregation ofsites where the measurement data associated with the aggregatedmeasurement site is a statistical aggregation of data associated witheach of the multiple sites. Moreover, each of these multiple sites mayinclude one or more measurement targets associated with a specimen orreference measurement.

As used herein, the term “wafer” generally refers to substrates formedof a semiconductor or non-semiconductor material. Examples include, butare not limited to, monocrystalline silicon, gallium arsenide, andindium phosphide. Such substrates may be commonly found and/or processedin semiconductor fabrication facilities. In some cases, a wafer mayinclude only the substrate (i.e., bare wafer). Alternatively, a wafermay include one or more layers of different materials formed upon asubstrate. One or more layers formed on a wafer may be “patterned” or“unpatterned.” For example, a wafer may include a plurality of dieshaving repeatable pattern features.

A “reticle” may be a reticle at any stage of a reticle fabricationprocess, or a completed reticle that may or may not be released for usein a semiconductor fabrication facility. A reticle, or a “mask,” isgenerally defined as a substantially transparent substrate havingsubstantially opaque regions formed thereon and configured in a pattern.The substrate may include, for example, a glass material such asamorphous SiO₂. A reticle may be disposed above a resist-covered waferduring an exposure step of a lithography process such that the patternon the reticle may be transferred to the resist.

One or more layers formed on a wafer may be patterned or unpatterned.For example, a wafer may include a plurality of dies, each havingrepeatable pattern features. Formation and processing of such layers ofmaterial may ultimately result in completed devices. Many differenttypes of devices may be formed on a wafer, and the term wafer as usedherein is intended to encompass a wafer on which any type of deviceknown in the art is being fabricated.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A metrology system comprising: an illuminationsource configured to provide an amount of illumination light to one ormore metrology targets; a detector configured to receive an amount ofcollected light from the one or more metrology targets in response tothe amount of illumination light; one or more computer systemsconfigured to: receive an amount of measurement data associated with thedetected light; and determine one or more parameters of a measurementmodel of the one or more metrology targets based on a fitting of themeasurement model to the amount of measurement data, wherein themeasurement model includes a first re-useable, parametric model of afirst sub-structure of the one or more metrology targets; and ametrology model building tool comprising computer-readable instructionsstored on a non-transitory, computer-readable medium, thecomputer-readable instructions comprising: code for causing the one ormore computer systems to receive an indication of a selection of thefirst re-useable, parametric model by a first user to describe at leasta portion of the one or more metrology targets, wherein the firstre-useable, parametric model includes multiple geometric elements and isfully defined by a first set of independent parameter values; and codefor causing the one or more computer systems to receive an indication ofa selection of the first set of independent parameter values.
 2. Themetrology system of claim 1, wherein the measurement model of the one ormore metrology targets is fully described by the first re-useable,parametric model.
 3. The metrology system of claim 1, thecomputer-readable instructions further comprising: code for causing theone or more computer systems to receive an indication of a selection ofa second re-usable, parametric model by the first user to describe asub-structure of the one or more metrology targets, wherein the secondre-useable, parametric model includes multiple geometric elements and isfully defined by a second set of independent parameter values; code forcausing the one or more computer systems to receive an indication of aselection of the second set of independent parameter values; code forcausing the one or more computer systems to determine a firstmeasurement model of the one or more metrology targets based at least inpart on a combination of the first and second re-useable, parametricmodels; and code for causing the one or more computer systems to storethe first measurement model in a memory.
 4. The metrology system ofclaim 1, wherein the selection of the first set of independent parametervalues that define the first re-useable, parametric model is made by thefirst user.
 5. The metrology system of claim 1, the computer-readableinstructions further comprising: code for causing the one or morecomputer systems to receive an output file generated by a processsimulation tool; and code for causing the one or more computer systemsto determine the first set of independent parameter values from theoutput file.
 6. The metrology system of claim 1, wherein a plurality ofdiscretization points of the first re-useable, parametric model of thefirst sub-structure are aligned with a plurality of discretizationpoints of the second re-useable, parametric model of the secondsub-structure within a floating point precision of the one or morecomputer systems.
 7. The metrology system of claim 1, thecomputer-readable instructions further comprising: code for causing theone or more computer systems to receive an indication of a selection ofthe first re-useable, parametric model by a second user to describe afirst sub-structure of a second semiconductor device; code for causingthe one or more computer systems to receive an indication of a selectionof a third re-usable, parametric model by the second user to describe asecond sub-structure of the second semiconductor device, wherein thethird re-useable, parametric model is fully defined by a third set ofindependent parameter values; code for causing the one or more computingsystems to determine a second measurement model based at least in parton a combination of the first and third re-useable, parametric models;and code for causing the one or more computing systems to store thesecond measurement model in a memory.
 8. The metrology system of claim1, the computer-readable instructions further comprising: code forcausing the one or more computing systems to receive an indication of aselection of the first measurement model of the one or more metrologytargets; code for causing the one or more computing systems to receivean indication of a selection of a third re-usable, parametric model,wherein the third re-useable, parametric model is fully defined by athird set of independent parameter values; code for causing the one ormore computing systems to determine a second measurement model based atleast in part on a combination of the first measurement model and thethird re-useable, parametric model; and code for causing the one or morecomputing systems to store the second measurement model in a memory. 9.The metrology system of claim 1, the computer-readable instructionsfurther comprising: code for causing the one or more computing systemsto hide a portion of a sub-structure of the one or more metrologytargets from display to the first user.
 10. The metrology system ofclaim 1, wherein the first re-useable, parametric model of at least aportion of the one or more metrology targets includes geometric featuresand interrelationships among geometric features that are specific to aparticular measurement application.
 11. A metrology system comprising:an illumination source configured to provide an amount of illuminationlight to one or more metrology targets; a detector configured to receivean amount of collected light from the one or more metrology targets inresponse to the amount of illumination light; one or more computersystems configured to: receive an amount of measurement data associatedwith the detected light; and determine one or more parameters of ameasurement model of the one or more metrology targets based on afitting of the measurement model to the amount of measurement data,wherein the measurement model includes a first re-useable, parametricmodel of at least a portion of the one or more metrology targets; and ametrology model building tool comprising computer-readable instructionsstored on a non-transitory, computer-readable medium, thecomputer-readable instructions comprising: code for causing a computerto receive an indication of a selection by a user of a plurality ofprimitive geometric modeling elements; code for causing the computer toreceive an indication from the user indicating a desired position ofeach of the plurality of primitive geometric modeling elements withrespect to the other primitive geometric modeling elements; code forcausing the computer to receive an indication from the user indicating adesired parameterization of the plurality of primitive geometricmodeling elements; code for causing the computer to determine the firstre-usable, parametric model based on a combination of the plurality ofprimitive geometric elements, wherein the first re-useable, parametricmodel is fully defined by a set of independent parameters associatedwith the desired parameterization; and code for causing the computer tostore the first re-useable, parametric model in a memory.
 12. Themetrology system of claim 11, wherein the determining of the firstre-usable, parametric model involves generating a set of constraintrelationships that fully integrate the plurality of primitive geometricmodeling elements into the re-useable, parametric model that is fullydefined by the set of independent parameters.
 13. The metrology systemof claim 11, the computer-readable instructions further comprising: codefor causing the computer to receive an indication of a selection by theuser of the first re-useable, parametric model; code for causing thecomputer to receive an indication of a selection by the user of a secondre-usable, parametric model of another portion of the one or moremetrology targets, wherein the second re-useable, parametric modelincludes multiple geometric elements and is fully defined by a secondset of independent parameter values; code for causing the computer todetermine the measurement model of the one or more metrology targetsbased at least in part on a combination of the first and secondre-useable, parametric models; and code for causing the computer tostore the measurement model in a memory.
 14. The metrology system ofclaim 13, the computer-readable instructions further comprising: codefor causing the computer to receive an indication from the first user ofthe first set of independent parameter values; and code for causing thefirst computer to receive an indication from the first user of thesecond set of independent parameter values.
 15. The metrology system ofclaim 13, the computer-readable instructions further comprising: codefor causing the computer to receive an output file generated by aprocess simulation tool; and code for causing the computer to determinethe first set of independent parameter values from the output file. 16.The metrology system of claim 13, wherein the measurement model is fullydefined by a third set of independent parameter values that includes atleast a portion of the first set of independent parameter values and thesecond set of independent parameter values.
 17. The metrology system ofclaim 11, the computer-readable instructions further comprising: codefor causing the computer to hide a portion of a sub-structure of the oneor more metrology targets from display to the user.
 18. A metrologysystem comprising: an illumination source configured to provide anamount of illumination light to one or more metrology targets; adetector configured to receive an amount of collected light from the oneor more metrology targets in response to the amount of illuminationlight; and one or more computer systems configured to: receive an amountof measurement data associated with the detected light; and determineone or more parameters of a measurement model of the one or moremetrology targets based on a fitting of the measurement model to theamount of measurement data, wherein the measurement model includes afirst re-useable, parametric model of a first sub-structure of the oneor more metrology targets, and wherein the first re-useable, parametricmodel includes multiple geometric elements and is fully defined by afirst set of independent parameter values.
 19. The metrology system ofclaim 18, wherein the measurement model also includes a secondre-useable, parametric model of a second sub-structure of the one ormore metrology targets, and wherein the second re-useable, parametricmodel includes multiple geometric elements and is fully defined by asecond set of independent parameter values.
 20. The metrology system ofclaim 19, wherein a plurality of discretization points of the firstre-useable, parametric model of the first sub-structure are aligned witha plurality of discretization points of the second re-useable,parametric model of the second sub-structure within a floating pointprecision of the one or more computer systems.